Masonry Magazine September 2007 Page. 39
Concrete Vibrator Usage
Once you've over-vibrated, the mixture must be removed and blended again. "You want it to be an even, smooth blend throughout the entire mix," Cuppett said. And to do this, manufacturers urge users to make sure the vibrator head is completely submerged. Otherwise, "you could overheat the bearings and either cause premature wear on the head or damage the head. So you want to make sure that the head is completely submerged at all times," Cuppett said.
In contrast, Steve Payne, general manager for Denver Concrete Vibrator, which manufactures flexible shaft, pneumatic and high-cycle concrete vibrators, as well as external form vibrators, said that the common mistake made on grouting jobs is under-vibration. He also noted that it is the changes in the code and the inspectors' interpretation of those codes that often lead to some confusion with these projects. To avoid these problems, he suggested the following guidelines: The consolidation technique in general should be five to 15 seconds at the bottom of the cell or lift, followed by pulling the vibrator up at a rate of about three inches per second. If the grout is placed in lifts, he said, it is necessary to penetrate the previous lift with the vibrator and then pull the vibrator up from there to effectively "knit" the lifts together. "Vibrator operators get a 'feel' for the job and adjust for grout consistency, et cetera, as they move along to accomplish the task properly," Payne said. "The pitch of the vibrator may actually change when the consolidation is complete, and the operator will see the surface appearance change and take on a sheen," he continued.
Payne added that if the radius of effect of the vibrator is too small for the cell, multiple insertions are required to ensure overlap of the fields of action and the elimination of voids where no vibration has taken place. The rule of thumb, he said, is that the field of action (or radius of effect) is about eight times the diameter of the vibrator head.
Conclusion
AS PAYNE NOTED so well, proper internal vibration increases the bond between the grout and the rebar in RMC. It also decreases the possibility of cold joints, honeycombing, segregation and excessive air, while adding strength to the finished product. The key to ensuring that all of your projects are grouted properly is keeping abreast of the changing standards and regulations.
Leonard suggested that continuing to educate mason contractors and other construction professionals on this issue is a good place to start. "The masonry industry, particularly the MCAA, does a good job at offering doses of knowledge that are timely to changes in our industry," he said. "Like any industry that has competition-and masonry is no exception - we have to stay current with the changes and our approach to those changes. I make sure that my field (sales) managers are certified in concrete masonry testing procedures, for instance. We have to be able to assist our customers and the industry when problems, particularly with testing, occur in the field. This ends up helping in the overall process and keeps jobs moving along."
Bennu Parts & Service
Made In U.S.A.
COMING SOON!
Continuous-Climb
Power Units
NEWS
Call or email for information about
our products:
* Power Units - Reconditioned & Used
* Wings & Towers - New & Used
* Multi-Function Systems/Hoists
* All Spare Parts
Bennu Parts & Service
Phone: 847-595-8444
www.bennuparts.com
info@bennuparts.com